Enhancement of Turbulent Shear Stress and Mass Transfer in Wall Turbulence Accompanied With Wall Blowing

2016 ◽  
Author(s):  
Yushi Okamura ◽  
Hideaki Sugioka ◽  
Yasuo Kawaguchi
Keyword(s):  
Mass Transfer ◽  
Shear Stress ◽  
Spatial Distribution ◽  
Solid Wall ◽  
Structural Parameters ◽  
Wall Turbulence ◽  
Experimental Result ◽  
Turbulent Shear ◽  
Eddy Structure ◽  
Turbulent Schmidt Number

Spatial distribution of velocity and mass concentration fluctuation in turbulent channel flow with wall blowing were simultaneously measured by PIV/PLIF. The recorded pictures were analyzed to clarify the turbulent momentum and mass transfer from statistical view point and from spatial evolution of coherent eddy structure. Experimental result revealed that the Reynold shear stress and turbulent intensity are enhanced as the blowing rate increasing. On the other hand, structural parameters based on local turbulence such as turbulent Schmidt number and a degree of turbulent anisotropy is not affected by wall blowing. In comparison without wall blowing, we found that the turbulent eddy structure locates apart from the wall. Besides, energy spectrum and swirling strength is also enhanced by wall blowing. It is associated with increase of resistance by wall blowing. Generally in wall turbulence, fluctuation motions are restricted by the presence of solid wall. But for the blowing from the wall relaxes this restriction and Reynolds shear stress is enhanced, which leads to enhancement of turbulent mass flux. Moreover, from results of spatial distribution of instantaneous fields, wall-blowing helps development of hairpin vortexes. It is concluded that development of hairpins leads to enhancement of turbulent mass transfer.

Cyclic modulation of Reynolds stresses and length scales in pulsed turbulent channel flow

1995 ◽  
Vol 451 (1941) ◽  
pp. 121-139 ◽  
Keyword(s):  
Shear Stress ◽  
Channel Flow ◽  
Structural Parameters ◽  
Turbulent Channel Flow ◽  
Wall Turbulence ◽  
Quadrant Analysis ◽  
Shear Stresses ◽  
Time Lags ◽  
Length Scales ◽  
Near Wall

Recent data obtained in an unsteady turbulent channel flow is reviewed. Results concerning the modulation characteristics of the Reynolds shear stresses, of the structural parameters and of the length scales inferred from unsteady spatial correlations are discussed. The close examination of both the amplitude and the phase shifts of the Reynolds shear stresses confirms the existence of three distinct inposed frequency regimes, namely the quasi-steady regime, the relaxation regime, in which the amplitudes decrease and which is accompanied by large time lags, and a subsequent third regime wherein the modulation characteristics change considerably. The fine structure of the near-wall turbulence response through quadrant analysis reveals large cyclic variations of the contributions of ejections and sweeps to the Reynolds shear stress. The reaction of the spanwise extent of the near-wall structures is investigated through the spanwise correlation coefficient between the wall shear stress and the streamwise velocity, and the resulting length scales. A temporal filtering of both signals shows that the inactive motions respond uniformly in the whole imposed frequency regime. A strong correlation is found between the modulation characteristics of the streak spacing and the ejection frequency.

PIV-PLIF Experiment on Modification of Turbulent Scalar Diffusion Near the Wall by Uniform Blowing

2015 ◽  
Author(s):  
Hideaki Sugioka ◽  
Zaiguo Fu ◽  
Takahiro Tsukahara ◽  
Yasuo Kawaguchi
Keyword(s):  
Mass Transfer ◽  
Mass Transfer Rate ◽  
Porous Wall ◽  
Industrial Applications ◽  
Wall Turbulence ◽  
Small Scale ◽  
Turbulence Energy ◽  
Turbulent Schmidt Number ◽  
Heat Transfers ◽  
Scalar Diffusion

The transfer phenomena of wall turbulence are associated with the quasi ordered vortex structures, which are developed from small scale vortices near the wall. How to change the turbulent motion and turbulent transfer by modifying the condition of near wall is important for academic and industrial applications in the control of mass and heat transfers. In this study, we examined experimentally the effect on changing mass transfer in channel turbulence by uniform blowing from a porous wall. We used PIV/PLIF simultaneous measurement by mixing fluorescent dye into blown fluids to observe the spatial evolution of mass transfer in turbulence and analyzed flow fields from the view point of turbulence statistics. It was found that blowing enhanced fluctuation of disturbance and along with it, the coefficients of skin friction and mass transfer rate were increased. On the other hand, the isotropy of turbulence and turbulent Schmidt number were almost not changed. We concluded that there are universality in redistribution of turbulence energy and similar relationship between momentum and mass transfer.

The Effects of Adverse Pressure Gradients on Momentum and Thermal Structures in Transitional Boundary Layers: Part 2—Fluctuation Quantities

1996 ◽  
Vol 118 (4) ◽  
pp. 728-736 ◽  
Author(s):  
S. P. Mislevy ◽  
T. Wang
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Transition Region ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Turbulent Shear ◽  
Wall Region ◽  
Pressure Gradients ◽  
Baseline Case ◽  
Near Wall

The effects of adverse pressure gradients on the thermal and momentum characteristics of a heated transitional boundary layer were investigated with free-stream turbulence ranging from 0.3 to 0.6 percent. Boundary layer measurements were conducted for two constant-K cases, K1 = −0.51 × 10−6 and K2 = −1.05 × 10−6. The fluctuation quantities, u′, ν′, t′, the Reynolds shear stress (uν), and the Reynolds heat fluxes (νt and ut) were measured. In general, u′/U∞, ν′/U∞, and νt have higher values across the boundary layer for the adverse pressure-gradient cases than they do for the baseline case (K = 0). The development of ν′ for the adverse pressure gradients was more actively involved than that of the baseline. In the early transition region, the Reynolds shear stress distribution for the K2 case showed a near-wall region of high-turbulent shear generated at Y+ = 7. At stations farther downstream, this near-wall shear reduced in magnitude, while a second region of high-turbulent shear developed at Y+ = 70. For the baseline case, however, the maximum turbulent shear in the transition region was generated at Y+ = 70, and no near-wall high-shear region was seen. Stronger adverse pressure gradients appear to produce more uniform and higher t′ in the near-wall region (Y+ < 20) in both transitional and turbulent boundary layers. The instantaneous velocity signals did not show any clear turbulent/nonturbulent demarcations in the transition region. Increasingly stronger adverse pressure gradients seemed to produce large non turbulent unsteadiness (or instability waves) at a similar magnitude as the turbulent fluctuations such that the production of turbulent spots was obscured. The turbulent spots could not be identified visually or through conventional conditional-sampling schemes. In addition, the streamwise evolution of eddy viscosity, turbulent thermal diffusivity, and Prt, are also presented.

Impact of fluid turbulent shear stress on failure surface of reservoir bank landslide

2018 ◽  
Vol 11 (22) ◽  
Author(s):  
Xuan Zhang ◽  
Liang Chen ◽  
Faming Zhang ◽  
Chengteng Lv ◽  
Yi feng Zhou
Keyword(s):  
Shear Stress ◽  
Failure Surface ◽  
Turbulent Shear ◽  
Turbulent Shear Stress

Turbulent Mass Transfer Simulations of Binary Electrolyte in Parallel-Plate Electrode Channel

2012 ◽  
Vol 550-553 ◽  
pp. 2014-2018
Author(s):  
Xiao Lan Zhou ◽  
Cai Xi Liu ◽  
Yu Hong Dong
Keyword(s):  
Mass Transfer ◽  
Turbulent Flows ◽  
Primary Objective ◽  
Wall Turbulence ◽  
Limiting Current ◽  
Solid Boundary ◽  
Wall Region ◽  
Schmidt Numbers ◽  
Near Wall ◽  
Turbulent Mass Transfer

Electrochemical mass transfer in turbulent flows and binary electrolytes is investigated. The primary objective is to provide information about mass transfer in the near-wall region between a solid boundary and a turbulent fluid flow at different Schmidt numbers. Based on the computational fluid dynamics and electrochemistry theories, a model for turbulent electrodes channel flow is established. The turbulent mass transfer in electrolytic processes has been predicted by the direct numerical simulation method under limiting current and galvanostatic conditions, we investigate mean concentration and the structure of the concentration fluctuating filed for different Schmidt numbers from 0.1 to 100 .The effect of different concentration boundary conditions at the electrodes on the near-wall turbulence statistics is also discussed.

scholarly journals ASAXS study of CaF2nanoparticles embedded in a silicate glass matrix

2014 ◽  
Vol 47 (1) ◽  
pp. 60-66 ◽  
Author(s):  
Armin Hoell ◽  
Zoltan Varga ◽  
Vikram Singh Raghuwanshi ◽  
Michael Krumrey ◽  
Christian Bocker ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Spatial Distribution ◽  
Glass Matrix ◽  
Structural Parameters ◽  
Pixel Detector ◽  
Oxyfluoride Glass ◽  
X Ray ◽  
X Ray Scattering ◽  
Silicate Glass Matrix

The formation and growth of nanosized CaF2crystallites by heat treatment of an oxyfluoride glass of composition 7.65Na2O–7.69K2O–10.58CaO–12.5CaF2–5.77Al2O3–55.8SiO2(wt%) was investigated using anomalous small-angle X-ray scattering (ASAXS). A recently developed vacuum version of the hybrid pixel detector Pilatus 1M was used for the ASAXS measurements below the CaK-edge of 4038 eV down to 3800 eV. ASAXS investigation allows the determination of structural parameters such as size and size distribution of nanoparticles and characterizes the spatial distribution of the resonant element, Ca. The method reveals quantitatively that the growing CaF2crystallites are surrounded by a shell of lower electron density. This depletion shell of growing thickness hinders and finally limits the growth of CaF2crystallites. Moreover, in samples that were annealed for 10 h and more, additional very small heterogeneities (1.6 nm diameter) were found.

scholarly journals Gas-solid and gas-liquid mass transfer: Effect of turbulent Schmidt number

2007 ◽  
Vol 13 (3) ◽  
pp. 167-168 ◽  
Author(s):  
Aleksandar Dudukovic ◽  
Rada Pjanovic
Keyword(s):  
Mass Transfer ◽  
Eddy Viscosity ◽  
Schmidt Number ◽  
Mass Transfer Rate ◽  
Transfer Effect ◽  
Transfer Coefficients ◽  
Mass Transfer Effect ◽  
Liquid Mass ◽  
Turbulent Schmidt Number ◽  
Liquid Mass Transfer

The scope of this paper is to explain effect of eddy viscosity and turbulent Schmidt number on mass transfer rate. New, theoretically based correlation for gas-liquid mass transfer coefficients are proposed.

Wall turbulence eddy structure control by a group of heating wires

2002 ◽  
Author(s):  
N. Jiang ◽  
Y. Lian ◽  
Wei Shu ◽  
Zhi Wang
Keyword(s):  
Wall Turbulence ◽  
Structure Control ◽  
Eddy Structure
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